The goal of this study is to determine the therapeutic role of hormone replacement therapy (HRT) to prevent visceral obesity in postmenopausal women. The hypothesis is that HRT will augment the loss of visceral fat in postmenopausal women who undergo a 6-month weight reduction program, and that HRT will be useful in preventing visceral fat regain in women who continue HRT after a one-year follow-up. In addition, the study will examine whether changes in visceral fat are predictive of alterations in insulin sensitivity. postmenopausal women with abdominal obesity will be randomly assigned to either HRT or placebo intervention. All women will participate in a 6-month program of exercise and dietary restriction designed to induce a moderate fat loss. Women will be re-examined after a one-year follow-up period. Total abdominal and visceral fat will be measured with CT, body composition with DXA, insulin sensitivity with an euglycemic/hyperinsulinemic clamp, and energy balance with indirect calorimetry and doubly-labeled water before and after the weight reduction program, and after the one-year follow-up.